The extraction of hydrocarbons from subterranean formations involves drilling a well and undertaking completion operations to transform the drilled well into a producing one. The completion process typically involves casing the wellbore to ensure that the well does not close in upon itself. The casing is typically steel piping that is cemented into place to line the well. In order to achieve production, the casing and cement must be perforated to allow for the flow of hydrocarbons into the wellbore, but still provide a suitable amount of support and protection for the well.
Stimulation techniques have been developed to further improve the efficiency of hydrocarbon extraction. One such technique is hydraulic fracturing (“fracking”) which involves the injection of highly pressurized fracking fluids through the perforated casing and into the formation. Injection of such fluids creates small fractures/fissures that extend substantially perpendicularly outwardly from the well into the formation, through which distantly-located hydrocarbons can thereby flow into, and thus flow therealong and into the wellbore for pumping to surface.
Generally, perforating and fracking a well have involved separate processes in which a well casing is first perforated followed by the injection of high pressure fracking fluid. Processes for perforating the well casing have included, for example, running a perforation gun into the wellbore to discharge high pressure jets of fluid to penetrate the casing at various locations, or to fire “shaped” explosive charges at various intervals along the wellbore into the sides of the casing to create the perforations. Once the perforations are formed, the fracking fluid is pumped into the well to fracture the formation in the region surrounding the wellbore and preferably in outwardly extending fissures which extend perpendicularly outwardly from the wellbore. Disadvantageously, however, apart from the additional time and expense of a two step discrete process of inserting the perforating gun, perforating, and removing such perforating gun before perforating can occur, such prior art methods are further unsatisfactory, since the problem with prior art devices and methods which separately perforate the well bore with perforating “guns” which use explosive charges, withdrawing the guns, and then inserting the fracking tool, is that the fracking tool does not necessarily align with the created perforations. Such prior art methods are thus for this reason as well unsatisfactory.
Specialized tools have been described to improve the efficiency of such methods. U.S. Pat. No. 7,337,844 describes a perforating and fracturing tool that perforates the well using a jetting sub and a plurality of jets which eject high pressure fluid to perforate the well casing. The device comprises a fluid distributor which may be selectively configured to communicate high pressure fluid to supply the perforating operation or to concurrently or simultaneously communicate the high pressure fluid to supply the fracturing operation. By diverting the fluid flow, perforating and fracturing operations can be achieved while keeping the device in the wellbore.
Other tools have been described which involve mechanically perforating the well casing. U.S. Pat. No. 2,638,801 teaches a casing perforator that is attachable to a drill string in driving connection with at least one rotating drill. The casing perforator is lowered into a pipe or well casing to drill ports into the casing, and fluid under high pressure is then passed down through the drill string through the perforator and out through the drill while the drill is within the ports. Fluid is discharged through the hollow interior of the drill to hydraulic passages out into the surrounding formation. In this way, the drilling of the casing and the fracking of the formation are accomplished consecutively while maintaining the perforator in one position.
Similarly, Russian Patent No. 2069741 describes a device for mechanical perforation of wells in which a pair of hydraulically actuated puncturing units are caused to extend radially outwardly from the tool to pierce the casing. Fluid jets built within the puncturing units inject fluid through these puncturing units and into the formation to open channels therein. In this way, the device can mechanically puncture the casing while simultaneously opening channels in the formation while maintaining the device in one position.
International Patent Publication No. WO 2012/098377 describes a perforating tool that utilizes a plurality of pistons that cooperatively operate to outwardly deploy a cutter block along tracks to enable large perforations to be cut into the well casing. Once the perforations are made, the cutter block is inwardly retracted to allow the work string to be lowered in order to position a packer apparatus below the perforated section of the well casing. With the work string in this position, high pressure pumping of hydraulic fracturing fluid can be commenced to conduct a hydraulic fracturing operation.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.